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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

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citric acid solution (100 grams of citric acid and 333 c.c. of ammonia, of
D = 0-910 to i litre), 20 c.c. of 10% sodium phosphate and 15 c.c. of cone,
ammonia solution (in this way the magnesia alone is precipitated as mag-
nesium ammonium phosphate, the other bases remaining in solution). The
liquid is well stirred for 5 minutes, left to stand for 2 hours and filtered
(best through a Gooch crucible), the precipitate being washed, calcined
and weighed as pyrophosphate ; this weight, multiplied by 360, gives the
percentage of MgO.

(6) MAGNESIUM AS OXIDE (Fortini's method).1 This method requires
a small calorimeter with a chamber unattackable by hydrochloric acid and
an accurate thermometer ; Tortelli's thermo-oleometer, described under
" Fatty Substances " (General Methods, 21), serves excellently for this

In the chamber of the thermo-oleometer are placed 25 c.c. of hydro-
chloric acid (equal volumes of acid D = 1-19 and water), and after a few
moments the temperature shown by the thermometer stirrer noted. An
exactly weighed amount of the magnesia (0-5-1-0 gram) is then added and
well mixed in until the temperature no longer rises. The total rise of tem-
perature is proportional to the heat of the reaction, when a given calorimeter
and a given quantity of acid are used. With Tortelli's thermo-oleometer
and the above quantity of hydrochloric acid, i gram of MgO gives a rise

of 37°-

The carbonates and other impurities of calcined magnesites give no
appreciable rise of temperature on reaction with hydrochloric acid, but
calcium oxide behaves exactly like magnesium oxide.

* *

Pure magnesia for pharmaceutical purposes or for chemical laboratories
should correspond with tests 1-4. Calcined magnesite for making magnesia
cements, dielectric or insulating materials, artificial stone, etc., should contain
little carbonate (losing not more than 5% on calcination), not more than 4%
of calcium oxide and 85-90% of magnesium oxide. That for metallurgical
use (refractory materials) does not contain carbonates and may contain marked
quantities of ferric oxide (up to 10%), as well as manganese oxide, lime, alumina
and silica.

MgCla + 6H20 = 203-34

Colourless, deliquescent crystals, soluble in water or alcohol. It may
contain sulphates and sodium salts more especially, and sometimes phos-
phates, heavy metals, lime and ammonia, these being tested for thus :

1.  Solubility.—3 grams should give a clear solution with 15 c.c. of
absolute alcohol if the salt is pure ;   any insoluble residue is tested for
sodium salts.

2.  Sulphates.—The i: 10 solution, acidified with hydrochloric acid, is
tested with barium chloride.

3.  Phosphates.—2 grams, dissolved in 40 c.c.  of 10% ammonium

1 Ann. Lab. Chim. Gabelle, Vol. VI, p. 509.
(a) TOTAL MAGNESIA (Meyeirheife.r's method). 5 grains of the; finely